Where Goshawks dare … tracking movements in lowland England

Once a widespread bird of British forests, the mighty Goshawk was almost completely wiped out in the UK by the start of the 1900s. However, small numbers managed to cling on despite extensive deforestation and relentless persecution. Adding to the bird’s fragile plight was the fate suffered by most other birds of prey in the mid-20th century, the deadly impacts of the pesticide DDT. Since the banning of this highly toxic chemical, Goshawks have slowly recovered, along with other raptors, despite unwanted attention from egg-collectors, falconers, and game managers.

Today, although far from common, Goshawks are showing signs of continued population and distribution growth and are now thought to number around 1,200 pairs across the UK. To better understand the dispersal and habits of young birds in their first winter, researchers at BTO carried out studies in two contrasting areas of lowland England: Norfolk/Suffolk and Gloucestershire.

Scientists attached state-of-the-art tracking devices to 29 individual Goshawk chicks at their nests, under special license. This allowed the researchers to map the movements of the juvenile birds as they headed out into the world after fledging. Would the youngsters move large distances in search of suitable woodland habitats, similar to where they had been raised, but uninhabited by other Goshawks? Or might they simply go the shortest distance from the nest site that would take them outside of their parents’ territory? Or would they do something else altogether?

Remarkably, having left their nest area, most of the fledged hawks moved a similar distance of around 10 km, to spend their first winter as independent birds. Each young Goshawk, on average, then established a territory of just under four square kilometres. One difference in habits, was the use of habitat. Compared to adult birds, both sexes were less reliant on dense forest-dominated environments. However, the large young females tended to stick to areas with access to significant tracts of woodland, while the smaller males showed a preference for areas where there was more farmland, interspersed with blocks of tree cover. This may be related to the prey type the differently sized birds require, with mixed habitat providing a greater density of the small to medium sized birds, favoured as food by the males.

After a period of time, as the Goshawks aged, they became inclined back towards denser forests where they would reside, like their parents, all year round.

Given the slow pace at which the species is increasing across the UK, and the relatively short dispersal distances covered by young birds, it may be some time before we see Goshawks nesting in urban parks, as they do in several other European countries. But, their seeming adaptability to utilise other habitats outside of the expected, established large forests, does suggest that expansion is highly probable. With reduced persecution and continued access to key prey such as Grey Squirrel and Woodpigeon, the future of these dynamic hunters as breeding British birds looks assured.

The tracks for three Breckland Goshawks are mapped below: two females (red and green), and a male (blue), as of the end of April 2018. All three were hatched in 2017.  The green female took a ~20-day tour of East Anglia from 16^th March before returning 'home'. Other females have shown similar patterns of behaviour.

Chick diet

A brief nest camera study of the prey items being fed to chicks revealled that Grey Squirrels contributed most of the items, with Woodpigeons and corvids (all species) being common victims too. Woodpigeons were probbaly the most important prey species in terms of biomass. The diet however, was broad and probably reflects availability, with rabbits being prominent at one nest that was located within close proximity to an active rabbit colony (summarised in Fig. 1).

goshawk_diet_summary.jpg

Acknowledgements

Funding support for this research was provided by Mark Constantine, Gloucestershire Raptor Monitoring Group, Richard Webb & Michael Wortley, The National Lottery Heritage Fund, and gifts in Wills to the British Trust for Ornithology. We would also like to thank the support of Forestry England or their cooperation and interest in this species throughout the project, and local recorders Bernard Pleasance and Simon Evans for their dedicated assistance and field input. Finally, we extend our special thanks to Dave Anderson for early advice, guidance and training. Tagging and Schedule 1 nest visits were carried out under strict licencing arrangements.